New Defender's Study Bible Notes

2:16this is that. Peter here assures these devout Jews that this strange set of phenomena (the wind, the cloven tongues like fire, the preaching in many languages) was not an occult pagan manifestation of some kind, but an actual fulfillment of an important Old Testament prophecy, as found in Joel 2:28-32.

2:17in the last days. This “last days” prophecy of Joel was fulfilled at Pentecost only in a precursive sense. Its complete fulfillment must await the time of the end (see its continuation in Joel 3). Thus Peter’s statement: “This is that” (Acts 2:16) should be understood in the sense of “This is like that.”